The present invention relates to a method of navigating from a starting location, especially an instantaneous position, to a destination, a routing algorithm of a navigational system for an apparatus of locomotion, in particular a motor vehicle, ship or airplane, calculating a route from starting location to destination via nodal points stored in a digital map. The present invention also relates to a navigational system for an apparatus of locomotion, especially a motor vehicle, ship or airplane, having an internal route memory, an internal navigation device connected to it, an internal digital map and a data communications device for communicating with an external off-board navigational system.
Navigational systems, such as those in motor vehicles, are based on digital maps carried along in read-only memories. Since all functional elements are located in the vehicle, these navigational systems are classified as autonomous navigational systems. Navigational systems are also known in which the routes are calculated outside the actual route guidance system. For example, the route to be traveled by the vehicle may be calculated in a traffic telematics center. These so-called off-board navigational systems have the advantage that the range of use is not limited right from the beginning by volume and state of updating of the digital maps carried along. On the other hand, the speed, convenience and precision of an autonomous navigational system can only be achieved by a communications effort which is economically not feasible at this time.
However, conventional navigational systems have the disadvantage that either a completely autonomous route calculation takes place, or a completely external or off-board route calculation takes place, each having the disadvantages described above.
An object of the present invention is to make available an improved navigation method and an improved navigational device of the kind named above, which will eliminate the disadvantages recited above.
To accomplish this, according to the present invention it is provided that, in a navigation method of the type named above, in the case in which at least one of the nodal points of the route to be calculated is not contained in an internal digital map stored internally in the navigation system, the part of the route, which includes exclusively nodal points of the internal digital map, is calculated by an internal routing algorithm on the basis of the internal digital map as the internally calculated part of the route, and the part of the route not including nodal points stored in the internal digital map is calculated by an external routing algorithm on the basis of a stored digital map that is external with respect to the navigation system, as the externally calculated part of the route, transitional nodal points from the externally calculated route to the internally calculated route, and/or vice versa, being determined.
This has the advantage that a hybrid navigation system is available, in which the detailed data of the internal digital map are used, as far as possible, for the route guidance, and only in ranges lying outside the internal digital map a route guidance is used on the basis of an externally stored digital map. Thereby, according to the present invention, the advantages of an autonomous navigational system, namely, a high route guidance accuracy are unified with the advantages of an off-board navigational system, namely, no range limitation based on the digital map. At the same time, the disadvantages of an autonomous navigational system, namely, conducting navigation exclusively within the internally stored map, as well as the disadvantages of an off-board navigational system, namely, high transmission costs due to the large data volumes to be transmitted, are avoided. Thus, the user has available to him the advantages of the xe2x80x9coff-boardxe2x80x9d navigational system and the autonomous navigational system under a uniform operating surface having the best possible functions of each part.
In a preferred specific embodiment, the complete route is first calculated by the external routing algorithm, is transmitted to the navigational system, and subsequently that portion of the route, which includes exclusively nodal points stored in the internal map is calculated, and the corresponding portion of the externally calculated route is replaced by the internally calculated portion of the route.
In order to reduce communications costs and transmitting time, the internal routing algorithm first generates the internally calculated route, transmits data concerning still missing portions of the route, especially still missing nodal points and interchange nodal points, to the external routing algorithm, the external routing algorithm calculates only the still missing route portions and transmits these to the navigational system.
In a preferred specific embodiment, the internally calculated portion of the route is stored in the navigational system in an internal route memory, and the externally calculated portion of the route is stored in the navigational system in an external route memory, whereby either an internal navigation algorithm of the navigational system conducts a route guidance based on the route in the internal route memory, or an external route guidance algorithm of the navigational system conducts a route guidance based on the route in the external route memory.
Expediently, on reaching a transitional nodal point, switching takes place from the internal route guidance algorithm to the external route guidance algorithm when the apparatus of locomotion leaves the range of the internal digital map, or switching from the external route guidance algorithm to the internal route guidance algorithm takes place when the apparatus of locomotion reaches the range of the internal digital map.
Actual data are attained at all times in the internal route memory as well as the external route memory, if, during route guidance, nodal points already reached or passed sections of the route, are identified in the internal route memory as well as the external route memory as taken care of or passed, or are canceled, independently of which route guidance algorithm just happens to be active.
For rapid assignment of nodal points to the internal map or the external map, and for rapid retrieval of the corresponding interchange nodal points, internal nodal points stored in the internal digital map as well as external nodal points located outside the range of the internal digital map are stored in a destination input memory of the navigational system, and at least one interchange nodal point is stored for predefined external nodal points, the interchange nodal point being an internal nodal point contained in the internal digital map.
In order to optimize the selection of the interchange nodes, the interchange nodal points are determined in a separate communications step between the navigational system and an off-board navigational system, which executes the external routing algorithm and stores the external digital map, using a data protocol in the light of geographical descriptions of nodal points lying outside the internal digital map.
In one advantageous specific embodiment, after the input of a destination lying outside the range of the internal digital map, the navigational system transmits the input destination and a version number of the internal digital map to an off-board navigational system, which executes the external routing algorithm and stores the external digital map, from which the off-board navigational system determines an interchange nodal point from these data, going from which to the input destination the externally calculated portion of the road is calculated by the external routing algorithm and transmitted to the navigational system.
Expediently, the navigational system transmits a list of possible interchange nodal points to an off-board navigational system which carries out the external routing algorithm and stores the external digital map, the off-board navigational system selecting at least one suitable interchange nodal point according to the externally calculated portion of the route and transmitting it to the navigational system along with the externally calculated portion of the routs.
In another preferred specific embodiment the calculation of the externally calculated portion of the route occurs when the apparatus of locomotion leaves an area of the internal digital map.
In a navigational system of the type named above, the present invention allows for an external route memory connected to a data communications device as well as an external route guidance device connected to the external route memory to be provided, a switching device being further provided, which optionally activates the external or internal route guidance device during route guidance, depending on whether the apparatus of locomotion is inside or outside the range of the internal digital map.
This has the advantage that a hybrid navigation system is available, in which the detailed data of the internal digital map are used, as far as possible, for route guidance, and only in ranges lying outside the internal digital map route guidance is used on the basis of an externally stored digital map. Thereby, according to the present invention, the advantages of an autonomous navigational system, namely, a high route guidance accuracy are unified with the advantages of an off-board navigational system, namely, no range limitation based on the digital map. At the same time, the disadvantages of an autonomous navigational system, namely, conducting navigation exclusively within the internally stored map, as well as the disadvantages of an off-board navigational system, namely, high transmission costs due to the large data volumes to be transmitted, are avoided. Thus, the user has available to him the advantages of the off-board navigational system and the autonomous navigational system under a uniform operating surface having the best possible functions of each part.
In another embodiment of the present invention, the internal route memory and the external route memory are combined in one single memory.